A tire condition monitoring apparatus is known as an apparatus that allows a driver to check the condition of the tires of a vehicle from the passenger compartment. The tire condition monitoring apparatus includes transmitters respectively attached to the wheel assemblies, and a receiver mounted on the vehicle. Each of the transmitters transmits transmission data to the receiver. The transmission data transmitted from the transmitter includes data indicating the condition of the tire. The receiver receives the transmission data to acquire the condition of the tire.
In the tire condition monitoring apparatus described above, it is preferable that the receiver can identify the tire to which the tire condition included in the transmission data corresponds. In other words, it is preferable that the receiver can identify the wheel assembly to which the transmitter that has transmitted the received transmission data is attached. This type of tire condition monitoring apparatus is disclosed in Patent Document 1.
The tire condition monitoring apparatus disclosed in Patent Document 1 is mounted on a vehicle including rotation angle detecting devices that detect the rotation angles of the wheel assemblies. When detecting that the rotation angle of the wheel assembly matches a specific angle, the transmitter transmits transmission data. The receiver obtains the rotation angle of each wheel assembly from the rotation angle detecting device upon reception of the transmission data. The receiver identifies the wheel assembly to which each of the transmitters is attached based on variation of the rotation angle of each wheel assembly obtained upon reception of the transmission data.
There is a null point, at which the transmission data transmitted from the transmitters mutually interferes depending on the kind of vehicle. In a case in which the specific angle at which the transmission data is transmitted matches the null point, the receiver cannot receive the transmission data transmitted at the specific angle. As a result, it may be impossible to identify the wheel assembly to which each of the transmitters is attached. Thus, multiple specific angles at which transmission data is transmitted are set in some cases.
In a case in which multiple specific angles are set, the rotation angles obtained upon reception of the transmission data are classified for each specific angle at which the transmission data is transmitted. Further, variation is obtained for each of the classified rotation angles.